Control of copolymer compositions

ABSTRACT

Methods of making copolymers are described.

RELATED APPLICATION INFORMATION

This application is a continuation and claims priority to U.S.application Ser. No. 15/980,478, filed on May 15, 2018, which is acontinuation of U.S. application Ser. No. 14/514,320, filed Oct. 14,2014, which is a continuation of U.S. application Ser. No. 13/187,243,filed on Jul. 20, 2011, which is a continuation of U.S. application Ser.No. 12/754,344, filed on Apr. 5, 2010, and claims priority to U.S.Provisional Application Ser. No. 61/166,608, filed on Apr. 3, 2009 andU.S. Provisional Application Ser. No. 61/247,321, filed on Sep. 30,2009, all of which are hereby incorporated by reference.

BACKGROUND

Glatiramer acetate (also known as copolymer-1 and marketed as the activeingredient in COPAXONE® by Teva Pharmaceutical Industries Ltd., Israel)is used in the treatment of the relapsing-remitting form of multiplesclerosis (RRMS). According to the COPAXONE® product label, glatirameracetate (GA) consists of the acetate salts of synthetic polypeptidescontaining four naturally occurring amino acids: L-glutamic acid,L-alanine, L-tyrosine, and L-lysine with a reported average molarfraction of 0.141, 0.427, 0.095, and 0.338, respectively. Chemically,glatiramer acetate is designated L-glutamic acid polymer with L-alanine,L-lysine and L-tyrosine, acetate (salt). Its structural formula is:

(Glu, Ala, Lys, Tyr)_(x).xCH₃COOH(C₅H₉NO₄.C₃H₇NO₂.C₆H₁₄N₂O₂.C₉H₁₁NO₃)_(x).xC₂H₄O₂ CAS-147245-92-9

SUMMARY OF THE INVENTION

The invention is based, at least in part, on the identification ofmethods for controlling the level of L-pyroGlutamic Acid (pyro-Glu) inglatiramer acetate (GA). Pyro-Glu is present in GA, and the ability tocontrol the level of pyro-Glu in GA is useful in controlling bothproduct and process quality in the manufacture of GA.

Described herein is a method for preparing a composition comprisingglatiramer acetate, comprising: polymerizing N-carboxy anhydrides ofL-alanine, benzyl-protected L-glutamic acid, trifluoroacetic acid (TFA)protected L-lysine and L-tyrosine to generate a protected copolymer(Intermediate-1); treating the protected copolymer to partiallydepolymerize the protected copolymer and deprotect benzyl protectedgroups thereby generating a partially depolymerized, benzyl-deprotectedproduct (Intermediate-2); treating the partially depolymerized productto deprotect TFA-protected lysines thereby generating a TFA-deprotectedproduct (Intermediate-3) and further processing the Intermediate-3 tocreate glatiramer acetate, wherein the improvement comprises: havingwater present during at least a portion of the depolymerization step.

Also described herein is a method for preparing a composition comprisingglatiramer acetate, comprising: polymerizing N-carboxy anhydrides ofL-alanine, benzyl-protected L-glutamic acid, trifluoroacetic acid (TFA)protected L-lysine and L-tyrosine to generate a protected copolymer(Intermediate-1); treating the protected copolymer to partiallydepolymerize the protected copolymer and deprotect benzyl protectedgroups thereby generating a partially depolymerized, benzyl-deprotectedproduct (Intermediate-2); and treating the partially depolymerizedproduct to deprotect TFA-protected lysines thereby generating aTFA-deprotected product (Intermediate-3); and further processing theIntermediate-3 to create glatiramer acetate, wherein the improvementcomprises: adjusting the water present during at least a portion of thedepolymerization step so that amount water is present during at least aportion of the depolymerization step is within a predetermined range.

Also described herein is a method for preparing a composition comprisingglatiramer acetate, comprising: polymerizing N-carboxy anhydrides ofL-alanine, benzyl-protected L-glutamic acid, trifluoroacetic acid (TFA)protected L-lysine and L-tyrosine to generate a protected copolymer(Intermediate-1); treating the protected copolymer to partiallydepolymerize the protected copolymer and deprotect benzyl protectedgroups thereby generating a partially depolymerized, benzyl-deprotectedproduct (Intermediate-2); treating the partially depolymerized,benzyl-deprotected product to deprotect TFA-protected lysines therebygenerating acetate TFA-deprotected product (Intermediate-3); and furtherprocessing Intermediate-3 to create glatiramer acetate, wherein theimprovement comprises: controlling the water present during at least aportion of the depolymerization step so that amount water is presentduring at least a portion of the depolymerization step is within apredetermined range.

In various embodiments of the forgoing methods: water is present,adjusted or controlled at the beginning of the depolymerization step;water is added during the depolymerization step; the water presentduring the depolymerization step is present within a predetermined range(e.g., the predetermined range is 4-25%, 5-25%, 4-20%, 4-16%, 7-15%,8-14%, 9-13%, 10-12%, 13-19%, 14-18% w/w against Intermediate-1); thedepolymerization proceeds for 16-64 hrs, preferably at least 25 hrs(e.g., 25-55 hrs, at least 30 hrs, 30-50 hrs, at least 40 hrs, 43-47hrs); the depolymerization reaction is carried out at 17-35° C., e.g.,18-30° C., 18-22° C.; the depolymerization step comprises contacting theprotected copolymer with a solution comprising phenol, HBr and aceticacid; the concentration of pyroglu in the purified glatiramer acetate is2000-7000 ppm (e.g., 2500-6000 ppm; 2500-5500 ppm; 3000-5000 ppm;3500-4500 ppm, 2400-6500 ppm); the Mp of the purified glatiramer acetateis 5,000-9,000 Da (e.g., 6,500-7,500 Da); in one embodiment water ispresent during the depolymerization step at 11.2% w/w againstIntermediate-1, the depolymerization proceeds for 43-47 hrs at 18-22° C.and the process produces purified glatiramer acetate in which pyro-Gluis present at 0.24-0.65% w/w (2400-6500 ppm). The improvement furthercomprises: preparing a pharmaceutical composition comprising at least aportion of the purified glatiramer acetate; and in some cases the methodfurther includes measuring the amount of water in the depolymerizationstep at least once.

Also described is a method for preparing a composition comprisingglatiramer acetate, comprising: polymerizing N-carboxy anhydrides ofL-alanine, benzyl-protected L-glutamic acid, trifluoroacetic acid (TFA)protected L-lysine and L-tyrosine to generate a protected copolymer;treating the protected copolymer to partially depolymerize the protectedcopolymer and deprotect benzyl protected groups thereby generating apartially depolymerized product; treating the partially depolymerizedproduct to deprotect TFA-protected lysines thereby generating aTFA-deprotected product; and processing the TFA-deprotected product tocreate glatiramer acetate, wherein water is present during at least aportion of the depolymerization step.

An additional method is a method for preparing a composition comprisingglatiramer acetate, comprising: polymerizing N-carboxy anhydrides ofL-alanine, benzyl-protected L-glutamic acid, trifluoroacetic acid (TFA)protected L-lysine and L-tyrosine to generate a protected copolymer;treating the protected copolymer to partially depolymerize the protectedcopolymer and deprotect benzyl protected groups thereby generating apartially depolymerized product; treating the partially depolymerizedproduct to deprotect TFA-protected lysines thereby generating glatirameracetate; and purifying the glatiramer acetate to create purifiedglatiramer acetate, wherein water is present during at least a portionof the depolymerization step within a predetermined range.

An additional described method is a method for preparing a compositioncomprising glatiramer acetate, comprising: polymerizing N-carboxyanhydrides of L-alanine, benzyl-protected L-glutamic acid,trifluoroacetic acid (TFA) protected L-lysine and L-tyrosine to generatea protected copolymer; treating the protected copolymer to partiallydepolymerize the protected copolymer and deprotect benzyl protectedgroups thereby generating a partially depolymerized product; treatingthe partially depolymerized product to deprotect TFA-protected lysinesthereby generating a TFA-deprotected product; and processing the aTFA-deprotected product to create glatiramer acetate, wherein the waterpresent during at least a portion of the depolymerization step iscontrolled to be within a predetermined range.

In various embodiments of the foregoing methods: water is present,adjusted or controlled at the beginning of the depolymerization step;water is added during the depolymerization step; the water presentduring the depolymerization step is present within a predetermined range(e.g., the predetermined range is 4-25%, 5-25%, 13-19%, 14-18% w/wagainst Intermediate-1); the depolymerization proceeds for at least 25hrs (e.g., at least 30 hrs or at least 40 hrs); the depolymerizationstep comprises contacting the protected copolymer with a solutioncomprising phenol, HBr and acetic acid; the concentration of pyroglu inthe purified glatiramer acetate is 2000-7000 ppm (e.g., 2500-6000 ppm;2500-5500 ppm; 3000-5000 ppm; 3500-4500 ppm, 2400-6500 ppm (0.24%-0.65%w/w); the the Mp of the purified glatiramer acetate is 5,000-9,000 Da(e.g., 6,500-7,500 Da); the improvement further comprises: preparing apharmaceutical composition comprising at least a portion of the purifiedglatiramer acetate; the step of treating the partially depolymerizedproduct to deprotect TFA-protected lysines comprises treating thedepolymerized product with piperidine; the protected copolymer isisolated and at least partially dried prior to treating the protectedcopolymer to partially depolymerize the protected copolymer anddeprotect benzyl protected groups; the partially depolymerized productis isolated and at least partially dried prior to the step of treatingthe partially depolymerized product to deprotect TFA-protected lysines;in some cases the method further includes measuring the amount of waterin the depolymerization step at least once.

As used herein, a “copolymer”, “amino acid copolymer” or “amino acidcopolymer preparation” is a heterogeneous mixture of polypeptidescomprising a defined plurality of different amino acids (typicallybetween 2-10, e.g., between 3-6, different amino acids). A copolymer maybe prepared from the polymerization of individual amino acids. The term“amino acid” is not limited to naturally occurring amino acids, but caninclude amino acid derivatives and/or amino acid analogs. For example,in an amino acid copolymer comprising tyrosine amino acids, one or moreof the amino acids can be a homotyrosine. Further, an amino acidcopolymer having one or more non-peptide or peptidomimetic bonds betweentwo adjacent residues is included within this definition.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 depicts the structure of pyro-Glu.

FIG. 2 is a graph depicting the results of studies on the effect of thepresence water in the depolymerization reaction used in glatirameracetate production.

DETAILED DESCRIPTION OF THE INVENTION

Other than a statement about molecular weight and amino acidcomposition, which are recited in the FDA-approved label for theproduct, the label and other available literature for COPAXONE® does notprovide detailed information about the physiochemical characteristics ofthe product. It has been previously found that Pyro-Glu (FIG. 1) is acomponent of Copaxone® (glatiramer acetate or GA) that is present withina predetermined range (U.S. Ser. No. 12/408,058). For example, in manycases the pyro-Glu content of a GA preparation can be between 2000 ppmand 7000 ppm or 2400-6500 ppm.

The production of GA entails polymerization of amino acids to produce amixture of peptides, referred to as Intermediate-1, followed by partialdepolymerization and deprotection of Intermediate-1 to yieldIntermediate-2. It has now been found that the level of pyro-Glu in GAcan be effectively controlled by controlling the water present duringthe depolymerization step of the GA manufacturing process, for example,by adjusting the water content at the beginning of and/or during thedepolymerization step, e.g., by adding water to a predetermined level atthe beginning or during the depolymerization step. Moreover, it has nowbeen found that by properly controlling (e.g., adjusting) the amount ofwater present during the depolymerization step and the duration of thedepolymerization step it is possible to produce GA with a specifiedpyro-Glu content and a specified peak molecular weight (Mp). In manycases it is specified to have the pyro-Glu content of copolymer or GA be2000 to 7000 ppm, e.g., 2500-5500 ppm, e.g., 3000-5000 ppm, e.g.,3500-4500 ppm, 2400-6500 ppm, and the water present during thedepolymerization reaction or added at the end of the depolymerizationreaction is preferably controlled or adjusted to achieve this specifiedpyro-Glu content. In many cases it is desirable to have the peakmolecular weight (Mp) of GA be 5,000 to 9,000 Da, e.g., 6,000 to 8,000Da, as measured as described in U.S. Pat. No. 7,074,580.

Manufacture of Glatiramer Acetate

Generally, the process for the manufacture of glatiramer acetateincludes the following steps:

-   -   Step 1: polymerization of N-carboxy anhydrides of L-alanine,        benzyl-protected L-glutamic acid, trifluoroacetic acid (TFA)        protected L-lysine and L-tyrosine (collectively referred to as        NCAs) to result in a protected copolymer (Intermediate-1),    -   Step 2: depolymerization and benzyl deprotection of        Intermediate-1 using hydrobromic acid in acetic acid (e.g.,        phenol treated 33% HBr/acetic acid), and    -   Step 3: deprotection of the TFA-protected lysines on        Intermediate-2 (e.g., by treatment with piperdine) to create        Intermediate-3, followed by processing to generate GA and        further purification and drying of the isolated GA drug        substance.

In Step 1 of GA manufacture, the NCAs are co-polymerized in apredetermined ratio using diethylamine as an initiator. Upon consumptionof the NCA components, the reaction mixture is quenched in water. Theresulting protected polymer (Intermediate-1) is isolated and dried. InStep 2 of GA manufacture, Intermediate-1 is treated with phenol-treated33% HBr in acetic acid (HBr/AcOH). This results in the cleavage of thebenzyl protecting group on the glutamic acids as well as cleavage ofpeptide bonds throughout the polymer. After a period of time thereaction is quenched with water, and the product polymer is isolated byfiltration and washed with water. The product polymer, Intermediate-2,has a reduced molecular weight relative to Intermediate-1.Intermediate-2 is dried before proceeding to Step 3. In Step 3,Intermediate-2 is treated with aqueous piperidine to remove thetrifluoroacetyl group on the lysines. The resulting copolymer,Intermediate-3, is subsequently purified usingdiafiltration/ultrafiltration and the resulting acetate salt is dried toproduce Glatiramer Acetate drug substance.

Methods for the manufacture of GA are described in the followingpublications: U.S. Pat. No. 3,849,550; WO 95/031990 and US 2007-0021324.

Control of pyro-Glu and Depolymerization with Water

As shown below, GA with a pyro-Glu content of about 4,000 ppm and a peakmolecular weight (Mp) about 7,000 Da can prepared by having waterpresent in the depolymerization reaction at about 16% w/w againstIntermediate-1. While the amount of water present is expressed hererelative to the amount Intermediate 1, the amount of water present canbe expressed in any convenient manner, for example: w/w against theweight of Intermediate-1 added to the depolymerization reaction; w/wagainst the weight of phenol used to treat the HBr/acetic acid added todepolymerization reaction; w/w against the total weight of HBr/aceticacid added to depolymerization reaction; v/v against the total volume ofHBr/acetic acid added to the depolymerization reaction; or w/w againstthe total weight of the depolymerization reaction. Thus, the amount ofwater present relative to HBr/AcOH on a v/v basis can be calculated fromthe amount of water present relative to Intermediate-1 on a w/w basis asfollows:

Vol_((water))/Vol_((HBR/AcOH))=(Wt_((water))/Wt_((Intermediate-1))×(Wt_((Intermediate-1))/Wt_((HBr/AcOH)))×(Wt_((HBr/AcOH))/Vol_((HBr/AcOH)))×(Vol_((water))/Wt_((water)))=(Wt_((water))/Wt_((Intermediate-1)))×(Wt_((Intermediate-1))/Wt_((HBr/AcOH)))×(Density_((HBr/AcOH))/Density_((water)))

The water present during the depolymerization reaction can include waterpresent in the Intermediate-1 added to the depolymerization reaction(e.g., by using Intermediate-1 that is not fully dried) and/or waterthat is added at the beginning or during the depolymerization reaction.Thus, the amount of water present during at least a portion of thedepolymerization reaction can be controlled by adding water to thereaction to achieve a predetermined level of water or by having acertain amount of water present in the Intermediate-1 added to thereaction or by a combination of adding water and having water present inthe Intermediate-1. Thus, the amount of water present can be controlledby simply having a reasonably consistent amount of water present in theIntermediate-1. Water can be added to the depolymerization reaction atany time, but is most often present at a predetermined level, e.g.,4-25%, 5-25%, 10-20%, 4-20%, 4-16%, 7-15%, 8-14%, 9-13%, 10-12%, 13-19%,14-18%, 15-17%, or 16% w/w against the weight of Intermediate-1, at thebeginning of the depolymerization reaction. Because the depolymerizationreaction can both consume and produce water, the amount of water presentcan change slightly over the course of the depolymerization reaction.

The amount of water present during the depolymerization step can impactthe pyro-Glu content and molecular weight of the resulting GA, as shownby the experiments described below. However, the amount of water presentduring the depolymerization step can vary over a reasonable range andstill be compatible with the production of GA having a desirablepyro-Glu content and molecular weight.

EXAMPLES Example 1

The effect of water present during the depolymerization step, Step 2, onthe pyro-Glu content and molecular weight of the resulting GA wasexamined as follows. Intermediate-1 was produced as described above anddivided between two depolymerization reactions (A and B). ForDepolymerization reaction A, no water was added. For Depolymerizationreaction B, water was added to 16% measured w/w against Intermediate-1.Depolymerization was allowed to proceed at 20° C. Aliquots removedperiodically from each reaction were quenched with water and furtherprocessed to produce GA. The pyro-Glu content (ppm), measured asdescribed below, and peak molecular weight (Mp) of each of the resultingGA samples were measured. The results of this analysis are shown in FIG.2. The molecular weight (Mp) scale (Da) is on the left axis, thepyro-Glu concentration scale (ppm) is on the right axis. The time ofDepolymerization reaction A (no added water) is on the upper horizontalaxis, and the time of Depolymerization reaction B (water present at 16%w/w against intermediate-1) is on the lower horizontal axis. The scaleof the graph is such that the horizontal line labeled “Midpoint ofdesired range of GPC-Mp (Da)/Midpoint of the desired range of pyroGlu(ppm)” indicates both one desirable Mp molecular weight (7,000 Da) andone desirable pyro-Glu concentration for GA (4,000 ppm). The lineslabeled MW_(A) and MW_(B) depict the Mp molecular weight of the GAproduced from material removed from Depolymerization reaction A andDepolymerization reaction B, respectively, at various time points. Thelines labeled Py_(A) and Py_(B) depict the concentration pyro-Glu in theGA produced from material removed from Depolymerization reaction A andDepolymerization reaction B, respectively, at various time points.

In the absence of added water, the desired combination of molecularweight and pyro-Glu concentration is not achieved. As can be seen inFIG. 2, after about 12 hours (scale on upper horizontal axis)Depolymerization reaction A (no added water) produces material thatyields GA having a desired pyro-Glu concentration (about 4,000 ppm), butthe molecular weight (Mp) of the GA is about 7,400 Da, above the desired7,000 Da. As can be also seen in FIG. 2, after about 26 hours (scale onupper horizontal axis) Depolymerization reaction A (no added water)produces material that yields GA having a desired Mp (about 7,000 Da),but the pyro-Glu concentration of the GA is greater than 6,000 ppm,which is above 4,000 ppm (the midpoint of the desired range). Incontrast, when water is added to the depolymerization reaction to 16%(w/w against Intermediate-1), the desired combination of molecularweight and pyro-Glu concentration is achieved. As can also be seen fromFIG. 2, after about 43 hours Depolymerization reaction B (16% water w/wagainst Intermediate-1) produces material that yields GA having adesired molecular weight (Mp about 7,000 Da) and a desired pyro-Gluconcentration (about 4,000 ppm).

Example 2

In the study described above pyro-Glu concentration of GA was measuredas follows. N-terminal pyro-Glu residues were cleaved using Pyrococcusfuriosus pyro-glutamate aminopeptidase. Pyro-Glu in the resultingenzymatic hydrolysate is isolated by reverse phase liquid chromatographyfollowed by detection at 200 nm using a reference standard curveprepared with known concentrations of L-Pyro-glutamate. Neurotensin (acommercially available polypeptide having 100% pyro-glutamate at theN-terminus) is assayed as a control to ensure the acceptability of thedigestion and adequacy of the HPLC separation. The chromatographicanalysis is performed using a Waters Atlantis C18 HPLC column and anisocratic mobile phase consisting of 100% Water, adjusted to pH 2.1 withphosphoric acid. Samples and Standards are held at 2-8° C. The peakcorresponding to the pyro-glutamate moiety elutes at a retention time ofapproximately 12 minutes. The direct measure of pyro-glutamate contentis on a w/w basis and the results are expressed as ppm (microgram/gram).

1. (canceled)
 2. A method for preparing a composition comprisingpurified glatiramer acetate having a pyroglutamate concentration of2000-7000 ppm and a Mp of 5000-9000 Da, comprising: polymerizingN-carboxy anhydrides of L-alanine, benzyl-protected L-glutamic acid,trifluoroacetic acid (TFA) protected L-lysine and L-tyrosine to generatea protected copolymer (Intermediate-1); treating the Intermediate-1 withHBr and acetic acid to partially depolymerize the protected copolymerand deprotect benzyl-protected L-glutamic acid thereby generating apartially depolymerized product; treating the partially depolymerizedproduct with piperidine to deprotect TFA-protected lysines therebygenerating glatiramer acetate; and purifying the glatiramer acetate tocreate purified glatiramer acetate having a pyro-Glu concentration of2000-7000 ppm and a Mp of 5000-9000 Da, wherein the amount of waterpresent during the entirety of the depolymerization reaction iscontrolled to be within 5-25% weight/weight against intermediate-1present at the beginning of the depolymerization reaction.
 3. The methodof claim 2 wherein the Intermediate-1 treated with HBr and acetic acidis not dry.
 4. The method of claim 2 further comprising adding water atthe start of the depolymerization reaction or during thedepolymerization reaction.
 5. The method of claim 2, wherein the amountof water present during the entirety of the depolymerization reaction iscontrolled to be within 8-14% w/w against Intermediate-1 present at thebeginning of the depolymerization reaction.
 6. The method of claim 2,wherein the amount of water present during the entirety of thedepolymerization reaction is controlled to be within 10-20% w/w againstIntermediate-1 present at the beginning of the depolymerizationreaction.
 7. The method of claim 2, wherein the amount of water presentduring the entirety of the depolymerization reaction is controlled to bewithin 7-15% w/w against Intermediate-1 present at the beginning of thedepolymerization reaction.
 8. The method of claim 2, wherein the amountof water present during the entirety of the depolymerization reaction iscontrolled to be within 9-13% w/w against Intermediate-1 present at thebeginning of the depolymerization reaction.
 9. The method of claim 2wherein the amount of water present during the entirety of thedepolymerization reaction is controlled to be within 10-12% w/w againstIntermediate-1 present at the beginning of the depolymerizationreaction.
 10. The method of claim 2, wherein the depolymerizationproceeds for at least 25 hrs.
 11. The method of claim 2, wherein thedepolymerization proceeds for at least 30 hrs.
 12. The method of claim2, wherein the depolymerization proceeds for at least 40 hrs.
 13. Themethod of claim 2, wherein the depolymerization reaction comprisescontacting the protected copolymer with a solution comprising phenol,HBr and acetic acid.
 14. The method of claim 2, wherein theconcentration of pyro-Glu in the purified glatiramer acetate is2500-5500 ppm.
 15. The method of claim 2, wherein the concentration ofpyro-Glu in the purified glatiramer acetate is 3000-5000 ppm.
 16. Themethod of claim 2, wherein the concentration of pyro-Glu in the purifiedglatiramer acetate is 3500-4500 ppm.
 17. The method of claim 2, whereinthe Mp of the purified glatiramer acetate is 6,500-7,500 Da.
 18. Themethod of claim 2, wherein the protected copolymer is isolated and atleast partially dried prior to treating the protected copolymer topartially depolymerize the protected copolymer and deprotect benzylprotected groups.
 19. The method of claim 2, further comprisingmeasuring the amount of water in the depolymerization reaction at leastonce.
 20. The method of claim 2, further comprising: preparing apharmaceutical composition comprising at least a portion of the purifiedglatiramer acetate.
 21. A method for preparing a drug product comprisingglatiramer acetate having a pyroglutamate concentration of 2000-7000 ppmand a Mp of 5000-9000 Da, comprising: polymerizing N-carboxy anhydridesof L-alanine, benzyl-protected L-glutamic acid, trifluoroacetic acid(TFA) protected L-lysine and L-tyrosine to generate a protectedcopolymer (Intermediate-1); treating the Intermediate-1 with HBr andacetic acid to partially depolymerize the protected copolymer anddeprotect benzyl-protected L-glutamic acid thereby generating apartially depolymerized product; treating the partially depolymerizedproduct with piperidine to deprotect TFA-protected lysines therebygenerating glatiramer acetate; purifying the glatiramer acetate tocreate purified glatiramer acetate having a pyro-Glu concentration of2000-7000 ppm and a Mp of 5000-9000 Da; preparing a pharmaceuticalcomposition comprising at least a portion of the purified glatirameracetate; processing at least a portion of the pharmaceutical compositionas a drug product, thereby preparing a drug product, wherein the amountof water present during the entirety of the depolymerization reaction iscontrolled to be within 5-25% weight/weight against intermediate-1present at the beginning of the depolymerization reaction.
 22. Themethod of claim 21 wherein the Intermediate-1 treated with HBr andacetic acid is not dry.
 23. The method of claim 21 further comprisingadding water at the start of the depolymerization reaction or during thedepolymerization reaction.
 24. The method of claim 21, wherein theamount of water present during the entirety of the depolymerizationreaction is controlled to be within 8-14% w/w against Intermediate-1present at the beginning of the depolymerization reaction.
 25. Themethod of claim 21, wherein the amount of water present during theentirety of the depolymerization reaction is controlled to be within10-20% w/w against Intermediate-1 present at the beginning of thedepolymerization reaction.
 26. The method of claim 21, wherein theamount of water present during the entirety of the depolymerizationreaction is controlled to be within 7-15% w/w against Intermediate-1present at the beginning of the depolymerization reaction.
 27. Themethod of claim 21, wherein the amount of water present during theentirety of the depolymerization reaction is controlled to be within9-13% w/w against Intermediate-1 present at the beginning of thedepolymerization reaction.
 28. The method of claim 21, wherein theamount of water present during the entirety of the depolymerizationreaction is controlled to be within 10-12% w/w against Intermediate-1present at the beginning of the depolymerization reaction.
 29. Themethod of claim 21, wherein the depolymerization proceeds for at least25 hrs.
 30. The method of claim 21, wherein the depolymerizationproceeds for at least 30 hrs.
 31. The method of claim 21, wherein thedepolymerization proceeds for at least 40 hrs.
 32. The method of claim21, wherein the depolymerization reaction comprises contacting theprotected copolymer with a solution comprising phenol, HBr and aceticacid.
 33. The method of claim 21, wherein the concentration of pyro-Gluin the purified glatiramer acetate is 2500-5500 ppm.
 34. The method ofclaim 21, wherein the concentration of pyro-Glu in the purifiedglatiramer acetate is 3000-5000 ppm.
 35. The method of claim 21, whereinthe concentration of pyro-Glu in the purified glatiramer acetate is3500-4500 ppm.
 36. The method of claim 21, wherein the Mp of thepurified glatiramer acetate is 6,500-7,500 Da.
 37. The method of claim21, wherein the protected copolymer is isolated and at least partiallydried prior to treating the protected copolymer to partiallydepolymerize the protected copolymer and deprotect benzyl protectedgroups.
 38. The method of claim 21, further comprising measuring theamount of water in the depolymerization reaction at least once.
 39. Themethod of claim 21, further comprising: preparing a pharmaceuticalcomposition comprising at least a portion of the purified glatirameracetate.